Process for producing ethanol using hydrogenation catalysts

ABSTRACT

The present invention relates to catalysts, to processes for making catalysts and to chemical processes employing such catalysts. The catalysts are preferably used for converting acetic acid to ethanol. The catalyst comprises a precious metal and one or more active metals on a modified support. The modified support may comprise cobalt tungstate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/595,365, filed on Aug. 27, 2012, which claims priority to U.S.Provisional App. No. 61/583,874, filed on Jan. 6, 2012, the entirety ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to catalysts, to processes for makingcatalysts, and to processes for producing ethanol from a feed streamcomprising a carboxylic acid and/or esters thereof in the presence ofthe inventive catalysts.

BACKGROUND OF THE INVENTION

Ethanol for industrial use is conventionally produced from petrochemicalfeed stocks, such as oil, natural gas, or coal, from feed stockintermediates, such as syngas, or from starchy materials or cellulosicmaterials, such as corn or sugar cane. Conventional methods forproducing ethanol from petrochemical feed stocks, as well as fromcellulosic materials, include the acid-catalyzed hydration of ethylene,methanol homologation, direct alcohol synthesis, and Fischer-Tropschsynthesis. Instability in petrochemical feed stock prices contributes tofluctuations in the cost of conventionally produced ethanol, making theneed for alternative sources of ethanol production all the greater whenfeed stock prices rise. Starchy materials, as well as cellulosicmaterial, are converted to ethanol by fermentation. However,fermentation is typically used for consumer production of ethanol, whichis suitable for fuels or human consumption. In addition, fermentation ofstarchy or cellulosic materials competes with food sources and placesrestraints on the amount of ethanol that can be produced for industrialuse.

Ethanol production via the reduction of alkanoic acids and/or othercarbonyl group-containing compounds has been widely studied, and avariety of combinations of catalysts, supports, and operating conditionshave been mentioned in the literature. The reduction of variouscarboxylic acids over metal oxides has been proposed by EP0175558 andU.S. Pat. No. 4,398,039. A summary some of the developmental efforts forhydrogenation catalysts for conversion of various carboxylic acids isprovided in Yokoyama, et al., “Carboxylic acids and derivatives” in:Fine Chemicals Through Heterogeneous Catalysis, 2001, 370-379.

U.S. Pat. No. 6,495,730 describes a process for hydrogenating carboxylicacid using a catalyst comprising activated carbon to support activemetal species comprising ruthenium and tin. U.S. Pat. No. 6,204,417describes another process for preparing aliphatic alcohols byhydrogenating aliphatic carboxylic acids or anhydrides or esters thereofor lactones in the presence of a catalyst comprising Pt and Re. U.S.Pat. No. 5,149,680 describes a process for the catalytic hydrogenationof carboxylic acids and their anhydrides to alcohols and/or esters inthe presence of a catalyst containing a Group VIII metal, such aspalladium, a metal capable of alloying with the Group VIII metal, and atleast one of the metals rhenium, tungsten or molybdenum. U.S. Pat. No.4,777,303 describes a process for the productions of alcohols by thehydrogenation of carboxylic acids in the presence of a catalyst thatcomprises a first component which is either molybdenum or tungsten and asecond component which is a noble metal of Group VIII on a high surfacearea graphitized carbon. U.S. Pat. No. 4,804,791 describes anotherprocess for the production of alcohols by the hydrogenation ofcarboxylic acids in the presence of a catalyst comprising a noble metalof Group VIII and rhenium. U.S. Pat. No. 4,517,391 describes preparingethanol by hydrogenating acetic acid under superatmospheric pressure andat elevated temperatures by a process wherein a predominantlycobalt-containing catalyst.

Existing processes suffer from a variety of issues impeding commercialviability including: (i) catalysts without requisite selectivity toethanol; (ii) catalysts which are possibly prohibitively expensiveand/or nonselective for the formation of ethanol and that produceundesirable by-products; (iii) required operating temperatures andpressures which are excessive; (iv) insufficient catalyst life; and/or(v) required activity for both ethyl acetate and acetic acid.

SUMMARY OF THE INVENTION

In a first embodiment, the invention is directed to a catalystcomprising a precious metal and one or more active metals on a modifiedsupport, wherein the modified support comprises (i) support material;(ii) a support modifier comprising a metal selected from the groupconsisting of tungsten, molybdenum, vanadium, niobium, and tantalum, and(iii) at least one of the one or more active metals. In one embodiment,the one or more active metals are selected from the group consisting ofcopper, iron, cobalt, vanadium, nickel, titanium, zinc, chromium,molybdenum, tungsten, tin, lanthanum, cerium, and manganese, andpreferably comprise cobalt and tin. Thus, at least one of the activemetals is part of the modified support as well as impregnated onto themodified support. In one embodiment, the precious metal is palladium,and the one or more active metals comprise cobalt and tin. In oneembodiment, the precious metal is platinum, and the one or more activemetals comprise cobalt and tin.

In a second embodiment, the invention is directed to a catalyst,comprising a support, a first theoretical layer formed on the supportcomprising one or more active metals, and a support modifier comprisinga metal selected from the group consisting of tungsten, molybdenum,vanadium, niobium, and tantalum; and a second theoretical layer formedon the first theoretical layer comprising a precious metal and at leastone of the active metals. By theoretical layers it is meant that thecomponents of respective layers are deposited in discrete steps.Notwithstanding the use of the term “layers” in the term “theoreticallayers,” it should be appreciated that multiple layers may or may not beformed on the catalyst support depending, for example, on the conditionsemployed in catalyst formation, on the amount of metal used in each stepand on the specific metals employed.

The precious metal is preferably selected from the group consisting ofrhodium, rhenium, ruthenium, platinum, palladium, osmium, iridium andgold. The one or more active metals optionally may be selected fromcopper, iron, cobalt, vanadium, nickel, titanium, zinc, chromium,molybdenum, tungsten, tin, lanthanum, cerium, and manganese, morepreferably cobalt and/or tin. For example, the catalyst may comprise theprecious metal in an amount from 0.1 to 5 wt. %, the cobalt in an amountfrom 0.5 to 20 wt. % and the tin in an amount from 0.5 to 20 wt. %,based on the total weight of the catalyst. In one aspect, the preciousmetal is palladium, and the one or more active metals comprise cobaltand tin, and in another aspect the precious metal is platinum, and theone or more active metals comprise cobalt and tin.

In one embodiment, the precious metal is present in an amount from 0.1to 5 wt. %, and the one or more active metals comprise a second metaland a third metal, wherein the second metal is present in an amount from0.5 to 20 wt. %, optionally 0.5 to 15 wt. %, and the third metal ispresent in an amount from 0.5 to 20 wt. %, optionally from 0.5 to 15 wt.%, based on the total weight of the catalyst. In one embodiment, themodified support comprises an oxide of tungsten, molybdenum or vanadiumin an amount from 0.1 to 40 wt. %, e.g., from 0.1 to 30 wt. % or from 10to 25 wt. %, of the metal based on the total weight of the catalyst.

The support itself preferably is a silicaceous support, e.g., silica, ora carbon support, e.g., carbon black or activated carbon, although anyof a variety of other supports may be used. In various embodiments, forexample, the support may be selected from silica, alumina, titania,silica/alumina, calcium metasilicate, pyrogenic silica, silica gel, highpurity silica, zirconia, carbon, zeolites and mixtures thereof. Thesupport modifier may comprise tungsten in a variety of forms, such as inthe form of tungsten oxide, or as a tungstate of an active metal. Forexample, the support modifier metal may comprise cobalt tungstate.Preferably, the support modifier does not comprise tin tungstate, eventhough the support modifier may comprise tin.

In another embodiment of the present invention is directed to a processfor producing ethanol, comprising contacting a feed stream comprisingacetic acid, and/or ethyl acetate, and hydrogen in a reactor at anelevated temperature in the presence of a catalyst, under conditionseffective to form ethanol, wherein the catalyst comprises a preciousmetal and one or more active metals on a modified support, wherein themodified support comprises (i) support material; (ii) a support modifiercomprising a metal selected from the group consisting of tungsten,molybdenum, vanadium, niobium, and tantalum, and (iii) at least one ofthe one or more active metals. The process may form a crude productcomprising the ethanol and ethyl acetate, and wherein the crude producthas an ethyl acetate steady state concentration from 0.1 to 40 wt. %,e.g. from 0.1 to 20 wt. %, or from 0.1 to 15 wt. %. The hydrogenationmay be performed in a vapor phase at a temperature from 125° C. to 350°C., a pressure of 10 kPa to 3000 kPa, and a hydrogen to acetic acid moleratio of greater than 4:1.

In a third embodiment, the present invention is directed to a catalystcomprising a precious metal selected from the group consisting ofrhodium, rhenium, ruthenium, platinum, palladium, osmium, iridium andgold and at least one active metal on a modified support, wherein the atleast one active metal is selected from the group consisting of copper,iron, cobalt, vanadium, nickel, titanium, zinc, chromium, molybdenum,tungsten, tin, lanthanum, cerium, and manganese, preferably cobalt andtin. The modified support comprises: support material, selected from thegroup consisting of silica, alumina, titania, silica/alumina, pyrogenicsilica, high purity silica, zirconia, carbon, zeolites and mixturesthereof; cobalt; tin; a support modifier comprising a metal selectedfrom the group consisting of tungsten, molybdenum, vanadium, niobium,and tantalum. In another embodiment, there is a process comprisingcontacting a feed stream comprising acetic acid and hydrogen in areactor at an elevated temperature in the presence of such catalyst.

In a fourth embodiment, the present invention is directed to a catalystcomprising a precious metal selected from the group consisting ofrhodium, rhenium, ruthenium, platinum, palladium, osmium, iridium andgold and at least one active metal on a modified support, wherein the atleast one active metal is selected from the group consisting of copper,iron, cobalt, vanadium, nickel, titanium, zinc, chromium, molybdenum,tungsten, tin, lanthanum, cerium, and manganese, wherein the modifiedsupport comprises: (i) support material, and (ii) cobalt tungstate. Inone embodiment, the modified support may further comprise tungstenoxide. In a further embodiment, the modified support may comprise tin.Preferably the modified support does not comprise tin tungstate, whichmay be suppressed by the presence of cobalt. In another embodiment,there is a process comprising contacting a feed stream comprising aceticacid and hydrogen in a reactor at an elevated temperature in thepresence of such catalyst having cobalt tungsten in the modifiedsupport.

In a fifth embodiment, the present invention is directed to ahydrogenation catalyst comprising a precious metal and cobalt tungstate,and having, after calcination, an x-ray diffraction patternsubstantially as shown in Table 5. Preferably, the hydrogenationcatalyst comprises a precious metal selected from the group consistingof rhodium, rhenium, ruthenium, platinum, palladium, osmium, iridium andgold and at least one active metal on a modified support, wherein the atleast one active metal is selected from the group consisting of copper,iron, cobalt, vanadium, nickel, titanium, zinc, chromium, molybdenum,tungsten, tin, lanthanum, cerium, and manganese, preferably cobalt andtin. The modified support may comprise a support material and cobalttungstate.

In a sixth embodiment, the present invention is directed to catalystcomprising a precious metal and cobalt tungstate, and having, aftercalcination, an x-ray diffraction pattern in which above 2θ=10°, thereis a local maximum having a characteristic full width at a half maximumat each of: a 2θ value in the range from 18.73 to 19.53°; a 2θ value inthe range from 24.25 to 25.43°; a 2θ value in the range from 30.29 to31.21°; a 2θ value in the range from 35.93 to 36.95°; a 2θ value in therange from 53.55 to 54.61°; a 2θ value in the range from 64.45 to65.67°. Preferably, the catalyst comprises a precious metal selectedfrom the group consisting of rhodium, rhenium, ruthenium, platinum,palladium, osmium, iridium and gold and at least one active metal on amodified support, wherein the at least one active metal is selected fromthe group consisting of copper, iron, cobalt, vanadium, nickel,titanium, zinc, chromium, molybdenum, tungsten, tin, lanthanum, cerium,and manganese. The modified support may comprise a support material andcobalt tungstate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood in view of the appendednon-limiting figures, in which:

FIG. 1 provides a non-limiting flow diagram for a process for forming acatalyst according to one embodiment of the present invention.

FIG. 2 is an XRD plot for the catalyst of Example 1.

DETAILED DESCRIPTION OF THE INVENTION

Catalyst Composition

The present invention is directed to catalyst compositions thatpreferably are suitable as hydrogenation catalysts, to processes forforming such catalysts, and to chemical processes employing suchcatalysts. The catalysts preferably comprise one or more active metalson a support, preferably a modified support, and may be suitable incatalyzing the hydrogenation of a carboxylic acid, e.g., acetic acid,and/or esters thereof, e.g., ethyl acetate, to the correspondingalcohol, e.g., ethanol.

In one embodiment, the inventive catalyst comprises a precious metal andone or more active metals on a support. Preferably the support is amodified support comprising a support material and a support modifiercomprising a metal selected from tungsten, molybdenum, vanadium, niobiumand tantalum. In one aspect, the modified support comprises one or moreof the active metals that are also disposed on the support, i.e., one ormore of the active metals are part of the modified support and alsodisposed on top of the modified support.

It has now been discovered that such catalysts are particularlyeffective as multifunctional hydrogenation catalysts capable ofconverting both carboxylic acids, such as acetic acid, and estersthereof, e.g., ethyl acetate, to their corresponding alcohol(s), e.g.,ethanol, under hydrogenation conditions. Thus, in another embodiment,the inventive catalyst comprises a precious metal and an active metal ona modified support, wherein the catalyst is effective for providing anacetic acid conversion greater than 20%, greater than 75% or greaterthan 90%, and an ethyl acetate conversion greater than 0%, greater than10% or greater than 20%.

Precious and Active Metals

The catalysts of the invention preferably include at least one preciousmetal impregnated on the catalyst support. The precious metal may beselected, for example, from rhodium, rhenium, ruthenium, platinum,palladium, osmium, iridium and gold. Preferred precious metals for thecatalysts of the invention include palladium, platinum, and rhodium. Theprecious metal preferably is catalytically active in the hydrogenationof a carboxylic acid and/or its ester to the corresponding alcohol(s).The precious metal may be in elemental form or in molecular form, e.g.,an oxide of the precious metal. The catalyst comprises such preciousmetals in an amount less than 5 wt. %, e.g., less than 3 wt. %, lessthan 2 wt. %, less than 1 wt. % or less than 0.5 wt. %. In terms ofranges, the catalyst may comprise the precious metal in an amount from0.05 to 10 wt. %, e.g. from 0.1 to 5 wt. %, or from 0.1 to 3 wt. %,based on the total weight of the catalyst. In some embodiments, themetal loading of the precious metal may be less than the metal loadingsof the one or more active metals.

In addition to the precious metal, the catalyst includes one or moreactive metals disposed on the modified support. In one embodiment, themodified support also comprises one or more active metals, such ascobalt and tin. Without being bound by theory, the active metals whenpart of the modified support may disperse the support modifier metal oroxide thereof on the support. An active metal is part of the modifiedsupport when it is impregnated and calcined on the support prior to theimpregnation or introduction of the precious metal to the modifiedsupport. The same active metals may be part of the modified support anddisposed on the support modifier. In particular, it may be preferred touse cobalt and tin.

As used herein, active metals refer to catalytically active metals thatimprove the conversion, selectivity and/or productivity of the catalystand may include precious or non-precious active metals. Thus, a catalystcomprising a precious metal and an active metal may include: (i) one (ormore) precious metals and one (or more) non-precious active metals, or(ii) may comprise two (or more) precious metals. Thus, precious metalsare included herein as exemplary active metals. Further, it should beunderstood that use of the term “active metal” to refer to some metalsin the catalysts of the invention is not meant to suggest that theprecious metal that is also included in the inventive catalysts is notcatalytically active.

In one embodiment, the one or more active metals included in thecatalyst are selected from the group consisting of copper, iron, cobalt,vanadium, nickel, titanium, zinc, chromium, molybdenum, tungsten, tin,lanthanum, cerium, manganese, any of the aforementioned precious metals,in particular rhenium, ruthenium, and gold, and combinations thereof.Preferably, however, the one or more active metals do not include anyprecious metals, and thus include copper, iron, cobalt, vanadium,nickel, titanium, zinc, chromium, molybdenum, tungsten, tin, lanthanum,cerium, manganese, and combinations thereof. More preferably, the one ormore active metals are selected from the group consisting of copper,iron, cobalt, nickel, chromium, molybdenum, tungsten and tin, and morepreferably the one or more active metals are selected from cobalt, tinand tungsten. In one embodiment, the active metal may comprise tin incombination with at least one other active metal. The one or more activemetals may be in elemental form or in molecular form, e.g., an oxide ofthe active metal, or a combination thereof.

The total weight of all the active metals, including the aforementionedprecious metal, present in the catalyst preferably is from 0.1 to 25 wt.%, e.g., from 0.5 to 15 wt. %, or from 1.0 to 10 wt. %. In oneembodiment, the catalyst may comprise from cobalt in an amount from 0.5to 20 wt. %, e.g., preferably from 4.1 to 20 wt. %, and tin in an amountfrom 0.5 to 20 wt. %, e.g., preferably from 0.5 to 3.5 wt. %. The activemetals for purposes of the present invention may be disposed on themodified support and may be part of the modified support. The totalweight of the active metal may include the combined weight of the metalin the modified support and the metal disposed on the modified support.Thus, for example, the modified support may comprise from 0.1 to 15 wt.%, e.g. from 0.5 to 10 wt. %, of the one or more active metals and theone or more active metals disposed on the modified support may bepresent in an amount from 0.1 to 15 wt. %, e.g., from 0.5 to 10 wt. %,provided that the total metal loading of the one or more active metalsis less than 25 wt. %. For purposes of the present specification, unlessotherwise indicated, weight percent is based on the total weight thecatalyst including metal and support.

In some embodiments, the catalyst contains at least two active metals inaddition to the precious metal. The at least two active metals may beselected from any of the active metals identified above, so long as theyare not the same as the precious metal or each other. Additional activemetals may also be used in some embodiments. Thus, in some embodiments,there may be multiple active metals on the support in addition to theprecious metal.

Preferred bimetallic (precious metal+active metal) combinations for someexemplary catalyst compositions include platinum/tin,platinum/ruthenium, platinum/rhenium, platinum/cobalt, platinum/nickel,palladium/ruthenium, palladium/rhenium, palladium/cobalt,palladium/copper, palladium/nickel, ruthenium/cobalt, gold/palladium,ruthenium/rhenium, ruthenium/iron, rhodium/iron, rhodium/cobalt,rhodium/nickel and rhodium/tin. In some embodiments, the catalystcomprises three metals on a support, e.g., one precious metal and twoactive metals. Exemplary tertiary combinations may includepalladium/rhenium/tin, palladium/rhenium/cobalt,palladium/rhenium/nickel, palladium/cobalt/tin, platinum/tin/palladium,platinum/tin/rhodium, platinum/tin/gold, platinum/tin/iridium,platinum/cobalt/tin, platinum/tin/copper, platinum/tin/chromium,platinum/tin/zinc, platinum/tin/nickel, rhodium/nickel/tin,rhodium/cobalt/tin and rhodium/iron/tin. In one preferred embodiment,the tertiary combination comprises cobalt or tin or both cobalt and tin.In some embodiments, the catalyst may comprise more than three metals onthe support.

When the catalyst comprises a precious metal and one active metal on asupport, the active metal is present in an amount from 0.1 to 20 wt. %,e.g., from 0.1 to 10 wt. %, or from 0.1 to 7.5 wt. %. When the catalystcomprises two or more active metals in addition to the precious metal,e.g., a first active metal and a second active metal, the first activemetal may be present in the catalyst in an amount from 0.05 to 20 wt. %,e.g. from 0.1 to 10 wt. %, or from 0.5 to 5 wt. %. The second activemetal may be present in an amount from 0.05 to 20 wt. %, e.g., from 0.1to 10 wt. %, or from 0.5 to 7.5 wt. %. If the catalyst further comprisesa third active metal, the third active metal may be present in an amountfrom 0.05 to 20 wt. %, e.g., from 0.05 to 10 wt. %, or from 0.05 to 7.5wt. %. When the second or third active metal is cobalt, in oneembodiment, the metal loading may be from 4.1 to 20 wt. %, e.g., from4.1 to 10 wt. % or from 4.1 to 7.5 wt. %. The active metals may bealloyed with one another or may comprise a non-alloyed metal solution, ametal mixture or be present as one or more metal oxides.

The preferred metal ratios may vary somewhat depending on the activemetals used in the catalyst. In some embodiments, the mole ratio of theprecious metal to the one or more active metals is from 10:1 to 1:10,e.g., from 4:1 to 1:4, from 2:1 to 1:2 or from 1.5:1 to 1:1.5. Inanother embodiment, the precious metal may be present in an amount from0.1 to 5 wt. %, the first active metal in an amount from 0.5 to 20 wt. %and the second active metal in an amount from 0.5 to 20 wt. %, based onthe total weight of the catalyst. In another embodiment, the preciousmetal is present in an amount from 0.1 to 5 wt. %, the first activemetal in an amount from 0.5 to 15 wt. % and the second active metal inan amount from 0.5 to 15 wt. %.

In one embodiment, the first and second active metals are present ascobalt and tin, and, when added to the catalyst together and calcinedtogether, are present at a cobalt to tin molar ratio from 6:1 to 1:6 orfrom 3:1 to 1:3. The cobalt and tin may be present in substantiallyequimolar amounts, when added to the catalyst together and calcinationtogether. In another embodiment, when cobalt is added to the supportmaterial initially and calcined as part of the modified support and tinis subsequently added to the modified support, it is preferred to have acobalt to tin molar that is greater than 4:1, e.g., greater than 6:1 orgreater than 11:1. Without being bound by theory the excess cobalt,based on molar amount relative to tin, may improve themultifunctionality of the catalyst.

Support Materials

The catalysts of the present invention comprise a suitable supportmaterial, preferably a modified support material. In one embodiment, thesupport material may be an inorganic oxide. In one embodiment, thesupport material may be selected from the group consisting of silica,alumina, titania, silica/alumina, pyrogenic silica, high purity silica,zirconia, carbon (e.g., carbon black or activated carbon), zeolites andmixtures thereof. Preferably, the support material comprises asilicaceous support material such as silica, pyrogenic silica, or highpurity silica. In one embodiment the silicaceous support material issubstantially free of alkaline earth metals, such as magnesium andcalcium. In preferred embodiments, the support material is present in anamount from 25 wt. % to 99 wt. %, e.g., from 30 wt. % to 98 wt. % orfrom 35 wt. % to 95 wt. %, based on the total weight of the catalyst.

In preferred embodiments, the support material comprises a silicaceoussupport material, e.g., silica, having a surface area of at least 50m²/g, e.g., at least 100 m²/g, or at least 150 m²/g. In terms of ranges,the silicaceous support material preferably has a surface area from 50to 600 m²/g, e.g., from 100 to 500 m²/g or from 100 to 300 m²/g. Highsurface area silica, as used throughout the application, refers tosilica having a surface area of at least 250 m²/g. For purposes of thepresent specification, surface area refers to BET nitrogen surface area,meaning the surface area as determined by ASTM D6556-04, the entirety ofwhich is incorporated herein by reference.

The preferred silicaceous support material also preferably has anaverage pore diameter from 5 to 100 nm, e.g., from 5 to 30 nm, from 5 to25 nm or from 5 to 10 nm, as determined by mercury intrusionporosimetry, and an average pore volume from 0.5 to 2.0 cm³/g, e.g.,from 0.7 to 1.5 cm³/g or from 0.8 to 1.3 cm³/g, as determined by mercuryintrusion porosimetry.

The morphology of the support material, and hence of the resultingcatalyst composition, may vary widely. In some exemplary embodiments,the morphology of the support material and/or of the catalystcomposition may be pellets, extrudates, spheres, spray driedmicrospheres, rings, pentarings, trilobes, quadrilobes, multi-lobalshapes, or flakes although cylindrical pellets are preferred.Preferably, the silicaceous support material has a morphology thatallows for a packing density from 0.1 to 1.0 g/cm³, e.g., from 0.2 to0.9 g/cm³ or from 0.3 to 0.8 g/cm³. In terms of size, the silica supportmaterial preferably has an average particle size, meaning the averagediameter for spherical particles or average longest dimension fornon-spherical particles, from 0.01 to 1.0 cm, e.g., from 0.1 to 0.7 cmor from 0.2 to 0.5 cm. Since the precious metal and the one or moreactive metals that are disposed on the support are generally in the formof very small metal (or metal oxide) particles or crystallites relativeto the size of the support, these metals should not substantially impactthe size of the overall catalyst particles. Thus, the above particlesizes generally apply to both the size of the support as well as to thefinal catalyst particles, although the catalyst particles are preferablyprocessed to form much larger catalyst particles, e.g., extruded to formcatalyst pellets.

Support Modifiers

The support material preferably comprises a support modifier. A supportmodifier may adjust the acidity of the support material. In oneembodiment, a support modifier comprises a metal selected from the groupconsisting of tungsten, molybdenum, vanadium, niobium, and tantalum. Themetal for the support modifier may be an oxide thereof. In oneembodiment, the support modifiers are present in an amount from 0.1 wt.% to 50 wt. %, e.g., from 0.2 wt. % to 25 wt. %, from 0.5 wt. % to 20wt. %, or from 1 wt. % to 15 wt. %, based on the total weight of thecatalyst. When the support modifier comprises tungsten, molybdenum, andvanadium, the support modifier may be present in an amount from 0.1 to40 wt. %, e.g., from 0.1 to 30 wt. % or from 0.1 to 20 wt. %, based onthe total weight of the catalyst.

As indicated, the support modifiers may adjust the acidity of thesupport. For example, the acid sites, e.g., Brønsted acid sites or Lewisacid sites, on the support material may be adjusted by the supportmodifier to favor selectivity to ethanol during the hydrogenation ofacetic acid and/or esters thereof. The acidity of the support materialmay be adjusted by optimizing surface acidity of the support material.The support material may also be adjusted by having the support modifierchange the pKa of the support material. Unless the context indicatesotherwise, the acidity of a surface or the number of acid sitesthereupon may be determined by the technique described in F. Delannay,Ed., “Characterization of Heterogeneous Catalysts”; Chapter III:Measurement of Acidity of Surfaces, p. 370-404; Marcel Dekker, Inc.,N.Y. 1984, the entirety of which is incorporated herein by reference. Ingeneral, the surface acidity of the support may be adjusted based on thecomposition of the feed stream being sent to the hydrogenation processin order to maximize alcohol production, e.g., ethanol production.

In some embodiments, the support modifier may be an acidic modifier thatincreases the acidity of the catalyst. Suitable acidic support modifiersmay be selected from the group consisting of: oxides of Group IVBmetals, oxides of Group VB metals, oxides of Group VIB metals, oxides ofGroup VIIB metals, oxides of Group VIII metals, aluminum oxides, andmixtures thereof. In one embodiment, the support modifier comprisesmetal selected from the group consisting of tungsten, molybdenum,vanadium, niobium, and tantalum.

In one embodiment, the acidic modifier may also include those selectedfrom the group consisting of WO₃, MoO₃, V₂O₅, VO₂, V₂O₃, Nb₂O₅, Ta₂O₅,FeO, Fe₃O₄, Fe₂O₃, Cr₂O₃, MnO₂, CoO, Co₂O₃, and Bi₂O₃. Reduced tungstenoxides or molybdenum oxides may also be employed, such as, for example,one or more of W₂₀O₅₈, WO₂, W₄₉O₁₁₉, W₅₀O₁₄₈, W₁₈O₄₉, Mo₉O₂₆, Mo₈O₂₃,MO₅O₁₄, Mo₁₇O₄₇, Mo₄O₁₁, or MoO₂. In one embodiment, the tungsten oxidemay be cubic tungsten oxide (H_(0.5)WO₃). It has now surprisingly andunexpectedly been discovered that the use of such metal oxide supportmodifiers in combination with a precious metal and one or more activemetals may result in catalysts having multifunctionality, and which maybe suitable for converting a carboxylic acid, such as acetic acid, aswell as corresponding esters thereof, e.g., ethyl acetate, to one ormore hydrogenation products, such as ethanol, under hydrogenationconditions.

In other embodiments, the acidic support modifiers include thoseselected from the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, Al₂O₃,B₂O₃, P₂O₅, and Sb₂O₃. Acidic support modifiers include those selectedfrom the group consisting of TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, and Al₂O₃.

In some embodiments, the acidic support modifier comprises a mixed metaloxide comprising at least one of the active metals and an oxide anion ofa Group IVB, VB, VIB, VIII metal, such as tungsten, molybdenum,vanadium, niobium or tantalum. The oxide anion, for example, may be inthe form of a tungstate, molybdate, vanadate, or niobate. Exemplarymixed metal oxides include cobalt tungstate, copper tungstate, irontungstate, zirconium tungstate, manganese tungstate, cobalt molybdate,copper molybdate, iron molybdate, zirconium molybdate, manganesemolybdate, cobalt vanadate, copper vanadate, iron vanadate, zirconiumvanadate, manganese vanadate, cobalt niobate, copper niobate, ironniobate, zirconium niobate, manganese niobate, cobalt tantalate, coppertantalate, iron tantalate, zirconium tantalate, and/or manganesetantalate. In one embodiment, the catalyst does not comprise tintungstate and is substantially free of tin tungstate. It has now beendiscovered that catalysts containing such mixed metal support modifiersmay provide the desired degree of multifunctionality at increasedconversion, e.g., increased ester conversion, and with reduced byproductformation, e.g., reduced diethyl ether formation.

In one embodiment, the catalyst comprises from 0.25 to 1.25 wt. %platinum, from 1 to 10 wt. % cobalt, and from 1 to 10 wt. % tin on asilica or a silica-alumina support material. The cobalt and tin may bedisposed on the support material and may be part of the modifiedsupport. The support material may comprise from 5 to 15 wt. % acidicsupport modifiers, such as WO₃, V₂O₅ and/or MoO₃. In one embodiment, theacidic modifier may comprise cobalt tungstate, e.g., in an amount from0.1 to 20 wt. %, or from 5 to 15 wt. %.

In some embodiments, the modified support comprises one or more activemetals in addition to one or more acidic modifiers. The modified supportmay, for example, comprise one or more active metals selected fromcopper, iron, cobalt, vanadium, nickel, titanium, zinc, chromium,molybdenum, tungsten, tin, lanthanum, cerium, and manganese. Forexample, the support may comprise an active metal, preferably not aprecious metal, and an acidic or basic support modifier. Preferably, thesupport modifier comprises a support modifier metal selected from thegroup consisting of tungsten, molybdenum, vanadium, niobium, andtantalum. In this aspect, the final catalyst composition comprises aprecious metal, and one or more active metals disposed on the modifiedsupport. In a preferred embodiment, at least one of the active metals inthe modified support is the same as at least one of the active metalsdisposed on the support. For example, the catalyst may comprise asupport modified with cobalt, tin and tungsten (optionally as WO₃,H_(0.5)WO₃, HWO₄, and/or as cobalt tungstate). In this example, thecatalyst further comprises a precious metal, e.g., palladium, platinumor rhodium, and at least one active metal, e.g., cobalt and/or tin,disposed on the modified support.

Without being by bound theory, it is believed that the presence of tintungstate on the modified support or catalyst tends to decreasecatalytic activity in the conversion of acetic acid to ethanol. Whenused on the modified support, tin does contribute to improved catalyticactivity and catalyst lifetime. However, when tin is present withtungsten, the undesirable tin tungstate species may form. To prevent theformation of tin tungstate, it has been found the use of cobalt mayinhibit the formation of tin tungstate. This allows the preferentialformation of cobalt tungstate over tin tungstate. In addition, thisallows the use of tin on the modified support to thus maintainsufficient catalyst activity and catalyst lifetime. In one embodiment,the modified support comprises cobalt tungstate and tin, but themodified support is substantially free of tin tungstate.

Processes for Making the Catalyst

The present invention also relates to processes for making the catalyst.Without being bound by theory, the process for making the catalyst mayimprove one or more of acetic acid conversion, ester conversion, ethanolselectivity and overall productivity. In one embodiment, the support ismodified with one or more support modifiers and the resulting modifiedsupport is subsequently impregnated with a precious metal and one ormore active metals to form the catalyst composition. For example, thesupport may be impregnated with a support modifier solution comprising asupport modifier precursor and optionally one or more active metalprecursors to form the modified support. After drying and calcination,the resulting modified support is impregnated with a second solutioncomprising precious metal precursor and optionally one or more of theactive metal precursors, followed by drying and calcination to form thefinal catalyst.

In this embodiment, the support modifier solution may comprise a supportmodifier metal precursor and one or more active metal precursors, morepreferably at least two active metal precursors. The precursorspreferably are comprised of salts of the respective metals in solution,which, when heated, are converted to elemental metallic form or to ametal oxide. Since, in this embodiment, two or more active metalprecursors are impregnated onto the support material simultaneouslyand/or sequentially with the support modifier precursor, one or more ofthe resulting active metals may interact with the support modifier metalat a molecular metal upon formation to form one or more polymetalliccrystalline species, such as cobalt tungstate. In other embodiments, oneor more of the active metals will not interact with the support modifiermetal precursor and are separately deposited on the support material,e.g., as discrete metal nanoparticles or as an amorphous metal mixture.Thus, the support material may be modified with one or more active metalprecursors at the same time that it is modified with a support modifiermetal, and the resulting active metals may or may not interact with thesupport modifier metal to form one or more polymetallic crystallinespecies.

In some embodiments, the support modifier may be added as particles tothe support material. For example, one or more support modifierprecursors, if desired, may be added to the support material by mixingthe support modifier particles with the support material, preferably inwater. When mixed it is preferred for some support modifiers to use apowdered material of the support modifiers. If a powdered material isemployed, the support modifier may be pelletized, crushed and sievedprior to being added to the support.

As indicated, in most embodiments, the support modifier preferably isadded through a wet impregnation step. Preferably, a support modifierprecursor to the support modifier may be used. Some exemplary supportmodifier precursors include alkali metal oxides, alkaline earth metaloxides, Group IIB metal oxides, Group IIIB metal oxides, Group IVB metaloxides, Group VB metal oxides, Group VIB metal oxides, Group VIIB metaloxides, and/or Group VIII metal oxides, as well as preferably aqueoussalts thereof.

Although the overwhelming majority of metal oxides and polyoxoion saltsare insoluble, or have a poorly defined or limited solution chemistry,the class of isopoly- and heteropolyoxoanions of the early transitionelements forms an important exception. These complexes may berepresented by the general formulae:[M_(m)O_(y)]^(p−) Isopolyanions[X_(x)M_(m)O_(y)]^(q−) (x≦m) Heteropolyanionswhere M is selected from tungsten, molybdenum, vanadium, niobium,tantalum and mixtures thereof, in their highest (d⁰, d¹) oxidationsstates. Such polyoxometalate anions form a structurally distinct classof complexes based predominately, although not exclusively, uponquasi-octahedrally-coordinated metal atoms. The elements that canfunction as the addenda atoms, M, in heteropoly- or isopolyanions may belimited to those with both a favorable combination of ionic radius andcharge and the ability to form d_(π)-p_(π) M-O bonds. There is littlerestriction, however, on the heteroatom, X, which may be selected fromvirtually any element other than the rare gases. See, e.g., M. T. Pope,Heteropoly and Isopoly Oxometalates, Springer Verlag, Berlin, 1983, 180;Chapt. 38, Comprehensive Coordination Chemistry, Vol. 3, 1028-58,Pergamon Press, Oxford, 1987, the entireties of which are incorporatedherein by reference.

Polyoxometalates (POMs) and their corresponding heteropoly acids (HPAs)have several advantages making them economically and environmentallyattractive. First, HPAs have a very strong approaching the superacidregion, Bronsted acidity. In addition, they are efficient oxidantsexhibiting fast reversible multielectron redox transformations underrather mild conditions. Solid HPAs also possess a discrete ionicstructure, comprising fairly mobile basic structural units, e.g.,heteropolyanions and countercations (H⁺, H₃O⁺, H₅O₂ ⁺, etc.), unlikezeolites and metal oxides.

In view of the foregoing, in some embodiments, the support modifierprecursor comprises a POM, which preferably comprises a metal selectedfrom the group consisting of tungsten, molybdenum, niobium, vanadium andtantalum. In some embodiments, the POM comprises a hetero-POM. Anon-limiting list of suitable POMs includes phosphotungstic acid(H—PW₁₂) (H₃PW₁₂O₄₀.nH₂O), ammonium metatungstate (AMT)((NH₄)₆H₂W₁₂O₄₀.H₂O), ammonium heptamolybdate tetrahydrate, (AHM)((NH₄)₆Mo₇O₂₄.4H₂O), silicotungstic acid hydrate (H—SiW₁₂)(H₄SiW₁₂O₄₀.H₂O), silicomolybdic acid (H—SiMo₁₂) (H₄SiMo₁₂O₄₀.nH₂O), andphosphomolybdic acid (H-PMo₁₂) (H₃PMo₁₂O₄₀.nH₂O).

The use of POM-derived support modifiers in the catalyst compositions ofthe invention has now surprising and unexpectedly been shown to providebi- or multi-functional catalyst functionality, desirably resulting inconversions for both acetic acid and byproduct esters such as ethylacetate, thereby rendering them suitable for catalyzing mixed feedscomprising, for example, acetic acid and ethyl acetate.

Impregnation of the precious metal and one or more active metals ontothe support, e.g., modified support, may occur simultaneously(co-impregnation) or sequentially. In simultaneous impregnation, the twoor more metal precursors are mixed together and added to the support,preferably modified support, together followed by drying and calcinationto form the final catalyst composition. With simultaneous impregnation,it may be desired to employ a dispersion agent, surfactant, orsolubilizing agent, e.g., ammonium oxalate or an acid such as acetic ornitric acid, to facilitate the dispersing or solubilizing of the first,second and/or optional third metal precursors in the event the twoprecursors are incompatible with the desired solvent, e.g., water.

In sequential impregnation, the first metal precursor may be first addedto the support followed by drying and calcining, and the resultingmaterial may then be impregnated with the second metal precursorfollowed by an additional drying step followed by a calcining step toform the final catalyst composition. Additional metal precursors (e.g.,a third metal precursor) may be added either with the first and/orsecond metal precursor or in a separate third impregnation step,followed by drying and calcination. Of course, combinations ofsequential and simultaneous impregnation may be employed if desired.

In embodiments where the precious metal and/or one or more activemetals, e.g., one or more of the first, second or third metals, areapplied to the catalyst sequentially, i.e., in multiple impregnationsteps, the catalyst may be said to comprise a plurality of “theoreticallayers.” For example, where a first metal is impregnated onto a supportfollowed by impregnation of a second metal, the resulting catalyst maybe said to have a first theoretical layer comprising the first metal anda second theoretical layer comprising the second metal. As discussedabove, in some aspects, more than one active metal precursor may beco-impregnated onto the support in a single step such that a theoreticallayer may comprise more than one metal or metal oxide. In anotheraspect, the same metal precursor may be impregnated in multiplesequential impregnation steps leading to the formation of multipletheoretical layers containing the same metal or metal oxide. In thiscontext, notwithstanding the use of the term “layers,” it will beappreciated by those skilled in the art that multiple layers may or maynot be formed on the catalyst support depending, for example, on theconditions employed in catalyst formation, on the amount of metal usedin each step and on the specific metals employed.

The use of a solvent, such as water, glacial acetic acid, a strong acidsuch as hydrochloric acid, nitric acid, or sulfuric acid, or an organicsolvent, is preferred in the support modification step, e.g., forimpregnating a support modifier precursor onto the support material. Thesupport modifier solution comprises the solvent, preferably water, asupport modifier precursor, and preferably one or more active metalprecursors. The solution is stirred and combined with the supportmaterial using, for example, incipient wetness techniques in which thesupport modifier precursor is added to a support material having thesame pore volume as the volume of the solution. Impregnation occurs byadding, optionally drop wise, a solution containing the precursors ofeither or both the support modifiers and/or active metals, to the drysupport material. Capillary action then draws the support modifier intothe pores of the support material. The thereby impregnated support canthen be formed by drying, optionally under vacuum, to drive off solventsand any volatile components within the support mixture and depositingthe support modifier on and/or within the support material. Drying mayoccur, for example, at a temperature from 50° C. to 300° C., e.g., from100° C. to 200° C. or about 120° C., optionally for a period from 1 to24 hours, e.g., from 3 to 15 hours or from 6 to 12 hours. The driedsupport may be calcined optionally with ramped heating, for example, ata temperature from 300° C. to 900° C., e.g., from 400° C. to 750° C.,from 500° C. to 600° C. or at about 550° C., optionally for a period oftime from 1 to 12 hours, e.g., from 2 to 10 hours, from 4 to 8 hours orabout 6 hours, to form the final modified support. Upon heating and/orthe application of vacuum, the metal(s) of the precursor(s) preferablydecompose into their oxide or elemental form. In some cases, thecompletion of removal of the solvent may not take place until thecatalyst is placed into use and/or calcined, e.g., subjected to the hightemperatures encountered during operation. During the calcination step,or at least during the initial phase of use of the catalyst, suchcompounds are converted into a catalytically active form of the metal ora catalytically active oxide thereof.

Once formed, the modified supports may be shaped into particles havingthe desired size distribution, e.g., to form particles having an averageparticle size in the range from 0.2 to 0.4 cm. The supports may beextruded, pelletized, tabletized, pressed, crushed or sieved to thedesired size distribution. Any of the known methods to shape the supportmaterials into desired size distribution can be employed. Alternatively,support pellets may be used as the starting material used to make themodified support and, ultimately, the final catalyst.

In one embodiment, the catalyst of the present invention may be preparedusing a bulk catalyst technique. Bulk catalysts may be formed byprecipitating precursors to support modifiers and one or more activemetals. The precipitating may be controlled by changing the temperature,pressure, and/or pH. In some embodiments, the bulk catalyst preparationmay use a binder. A support material may not be used in a bulk catalystprocess. Once precipitated, the bulk catalyst may be shaped by sprayingdrying, pelleting, granulating, tablet pressing, beading, or pilling.Suitable bulk catalyst techniques may be used such as those described inKrijn P. de Jong, ed., Synthesis of Solid Catalysts, Wiley, (2009), pg.308, the entire contents and disclosure of which is incorporated byreference.

In one embodiment, the precious metal and one or more active metals areimpregnated onto the support, preferably onto any of the above-describedmodified supports. A precursor of the precious metal preferably is usedin the metal impregnation step, such as a water soluble compound orwater dispersible compound/complex that includes the precious metal ofinterest. Similarly, precursors to one or more active metals may also beimpregnated into the support, preferably modified support. Depending onthe metal precursors employed, the use of a solvent, such as water,glacial acetic acid, nitric acid or an organic solvent, may be preferredto help solubilize one or more of the metal precursors.

In one embodiment, separate solutions of the metal precursors areformed, which are subsequently blended prior to being impregnated on thesupport. For example, a first solution may be formed comprising a firstmetal precursor, and a second solution may be formed comprising thesecond metal precursor and optionally the third metal precursor. Atleast one of the first, second and optional third metal precursorspreferably is a precious metal precursor, and the other(s) arepreferably active metal precursors (which may or may not compriseprecious metal precursors). Either or both solutions preferably comprisea solvent, such as water, glacial acetic acid, hydrochloric acid, nitricacid or an organic solvent.

In one exemplary embodiment, a first solution comprising a first metalhalide is prepared. The first metal halide optionally comprises a tinhalide, e.g., a tin chloride such as tin (II) chloride and/or tin (IV)chloride. Optionally, a second metal precursor, as a solid or as aseparate solution, is combined with the first solution to form acombined solution. The second metal precursor, if used, preferablycomprises a second metal oxalate, acetate, halide or nitrate, e.g.,cobalt nitrate. The first metal precursor optionally comprises an activemetal, optionally copper, iron, cobalt, nickel, chromium, molybdenum,tungsten, or tin, and the second metal precursor, if present, optionallycomprises another active metal (also optionally copper, iron, cobalt,nickel, chromium, molybdenum, tungsten, or tin). A second solution isalso prepared comprising a precious metal precursor, in this embodimentpreferably a precious metal halide, such as a halide of rhodium,rhenium, ruthenium, platinum or palladium. The second solution iscombined with the first solution or the combined solution, depending onwhether the second metal precursor is desired, to form a mixed metalprecursor solution. The resulting mixed metal precursor solution maythen be added to the support, optionally a modified support, followed bydrying and calcining to form the final catalyst composition as describedabove. The resulting catalyst may or may not be washed after the finalcalcination step. Due to the difficulty in solubilizing some precursors,it may be desired to reduce the pH of the first and/or second solutions,for example by employing an acid such as acetic acid, hydrochloric acidor nitric acid, e.g., 6 to 10 M HNO₃.

In another aspect, a first solution comprising a first metal oxalate isprepared, such as an oxalate of copper, iron, cobalt, nickel, chromium,molybdenum, tungsten, or tin. In this embodiment, the first solutionpreferably further comprises an acid such as acetic acid, hydrochloricacid, phosphoric acid or nitric acid, e.g., 6 to 10 M HNO₃. Optionally,a second metal precursor, as a solid or as a separate solution, iscombined with the first solution to form a combined solution. The secondmetal precursor, if used, preferably comprises a second metal oxalate,acetate, halide or nitrate, and preferably comprises an active metal,also optionally copper, iron, cobalt, nickel, chromium, molybdenum,tungsten, or tin. A second solution is also formed comprising a preciousmetal oxalate, for example, an oxalate of rhodium, rhenium, ruthenium,platinum or palladium, and optionally further comprises an acid such asacetic acid, hydrochloric acid, phosphoric acid or nitric acid, e.g., 6to 10 M HNO₃. The second solution is combined with the first solution orthe combined solution, depending on whether the second metal precursoris desired, to form a mixed metal precursor solution. The resultingmixed metal precursor solution may then be added to the support,optionally a modified support, followed by drying and calcining to formthe final catalyst composition as described above. The resultingcatalyst may or may not be washed after the final calcination step.

In one embodiment, the impregnated support, optionally impregnatedmodified support, is dried at a temperature from 100° C. to 140° C.,from 110° C. to 130° C., or about 120° C., optionally from 1 to 12hours, e.g., from 2 to 10 hours, from 4 to 8 hours or about 6 hours. Ifcalcination is desired, it is preferred that the calcination temperatureemployed in this step is less than the calcination temperature employedin the formation of the modified support, discussed above. The secondcalcination step, for example, may be conducted at a temperature that isat least 50° C., at least 100° C., at least 150° C. or at least 200° C.less than the first calcination step, i.e., the calcination step used toform the modified support. For example, the impregnated catalyst may becalcined at a temperature from 200° C. to 500° C., from 300° C. to 400°C., or about 350° C., optionally for a period from 1 to 12 hours, e.g.,from 2 to 10 hours, from 4 to 8 hours or about 6 hours.

In one embodiment, ammonium oxalate is used to facilitate solubilizingof at least one of the metal precursors, e.g., a tin precursor, asdescribed in U.S. Pat. No. 8,211,821, the entirety of which isincorporated herein by reference. In this aspect, the first metalprecursor optionally comprises an oxalate of a precious metal, e.g.,rhodium, palladium, or platinum, and a second metal precursor optionallycomprises an oxalate tin. Another active metal precursor, if desired,comprises a nitrate, halide, acetate or oxalate of chromium, copper, orcobalt. In this aspect, a solution of the second metal precursor may bemade in the presence of ammonium oxalate as solubilizing agent, and thefirst metal precursor may be added thereto, optionally as a solid or aseparate solution. If used, the third metal precursor may be combinedwith the solution comprising the first precursor and tin oxalateprecursor, or may be combined with the second metal precursor,optionally as a solid or a separate solution, prior to addition of thefirst metal precursor. In other embodiments, an acid such as aceticacid, hydrochloric acid or nitric acid may be substituted for theammonium oxalate to facilitate solubilizing of the tin oxalate. Theresulting mixed metal precursor solution may then be added to thesupport, optionally a modified support, followed by drying and calciningto form the final catalyst composition as described above.

The specific precursors used in the various embodiments of the inventionmay vary widely. Suitable metal precursors may include, for example,metal halides, amine solubilized metal hydroxides, metal nitrates ormetal oxalates. For example, suitable compounds for platinum precursorsand palladium precursors include chloroplatinic acid, ammoniumchloroplatinate, amine solubilized platinum hydroxide, platinum nitrate,platinum tetra ammonium nitrate, platinum chloride, platinum oxalate,palladium nitrate, palladium tetra ammonium nitrate, palladium chloride,palladium oxalate, sodium palladium chloride, sodium platinum chloride,and platinum ammonium nitrate, Pt(NH₃)₄(NO₄)₂. Generally, both from thepoint of view of economics and environmental aspects, aqueous solutionsof soluble compounds of platinum and palladium are preferred. In oneembodiment, the precious metal precursor is not a metal halide and issubstantially free of metal halides, while in other embodiments, asdescribed above, the precious metal precursor is a halide.

In another example, the second and third metals are co-impregnated withthe precursor to WO₃ on the support, optionally forming a mixed oxidewith WO₃, e.g., cobalt tungstate, followed by drying and calcination.The resulting modified support may be impregnated, preferably in asingle impregnation step or multiple impregnation steps, with one ormore of the first, second and third metals, followed by a second dryingand calcination step. In this manner, cobalt tungstate may be formed onthe modified support. Again, the temperature of the second calciningstep preferably is less than the temperature of the first calciningstep.

Use of Catalyst to Hydrogenate Acetic Acid

One advantage of catalysts of the present invention is the stability oractivity of the catalyst for producing ethanol. Accordingly, it can beappreciated that the catalysts of the present invention are fullycapable of being used in commercial scale industrial applications forhydrogenation of acetic acid, particularly in the production of ethanol.In particular, it is possible to achieve such a degree of stability suchthat catalyst activity will have a rate of productivity decline that isless than 6% per 100 hours of catalyst usage, e.g., less than 3% per 100hours or less than 1.5% per 100 hours. Preferably, the rate ofproductivity decline is determined once the catalyst has achievedsteady-state conditions.

After the washing, drying and calcining of the catalyst is completed,the catalyst may be reduced in order to activate it. Reduction iscarried out in the presence of a reducing gas, preferably hydrogen. Thereducing gas is optionally continuously passed over the catalyst at aninitial ambient temperature that is increased up to 400° C. In oneembodiment, the reduction is carried out after the catalyst has beenloaded into the reaction vessel where the hydrogenation will be carriedout.

In one embodiment the invention is to a process for producing ethanol byhydrogenating a feed stream comprising compounds selected from aceticacid, ethyl acetate and mixtures thereof in the presence of any of theabove-described catalysts. One particular preferred reaction is to makeethanol from acetic acid. The hydrogenation reaction may be representedas follows:HOAc+2H₂→EtOH+H₂OIn some embodiments, the catalyst may be characterized as a bifunctionalcatalyst in that it effectively catalyzes the hydrogenation of aceticacid to ethanol as well as the conversion of ethyl acetate to one ormore products, preferably ethanol.

The raw materials, acetic acid and hydrogen, fed to the reactor used inconnection with the process of this invention may be derived from anysuitable source including natural gas, petroleum, coal, biomass, and soforth. As examples, acetic acid may be produced via methanolcarbonylation, acetaldehyde oxidation, ethane oxidation, oxidativefermentation, and anaerobic fermentation. Methanol carbonylationprocesses suitable for production of acetic acid are described in U.S.Pat. Nos. 7,208,624; 7,115,772; 7,005,541; 6,657,078; 6,627,770;6,143,930; 5,599,976; 5,144,068; 5,026,908; 5,001,259; and 4,994,608,the entire disclosures of which are incorporated herein by reference.Optionally, the production of ethanol may be integrated with suchmethanol carbonylation processes.

As petroleum and natural gas prices fluctuate becoming either more orless expensive, methods for producing acetic acid and intermediates suchas methanol and carbon monoxide from other carbon sources have drawnincreasing interest. In particular, when petroleum is relativelyexpensive, it may become advantageous to produce acetic acid fromsynthesis gas (“syngas”) that is derived from other available carbonsources. U.S. Pat. No. 6,232,352, the entirety of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant, the large capital costs associated with CO generationfor a new acetic acid plant are significantly reduced or largelyeliminated. All or part of the syngas is diverted from the methanolsynthesis loop and supplied to a separator unit to recover CO, which isthen used to produce acetic acid. In a similar manner, hydrogen for thehydrogenation step may be supplied from syngas.

In some embodiments, some or all of the raw materials for theabove-described acetic acid hydrogenation process may be derivedpartially or entirely from syngas. For example, the acetic acid may beformed from methanol and carbon monoxide, both of which may be derivedfrom syngas. The syngas may be formed by partial oxidation reforming orsteam reforming, and the carbon monoxide may be separated from syngas.Similarly, hydrogen that is used in the step of hydrogenating the aceticacid to form the crude ethanol product may be separated from syngas. Thesyngas, in turn, may be derived from variety of carbon sources. Thecarbon source, for example, may be selected from the group consisting ofnatural gas, oil, petroleum, coal, biomass, and combinations thereof.Syngas or hydrogen may also be obtained from bio-derived methane gas,such as bio-derived methane gas produced by landfills or agriculturalwaste.

Biomass-derived syngas has a detectable ¹⁴C isotope content as comparedto fossil fuels such as coal or natural gas. An equilibrium forms in theEarth's atmosphere between constant new formation and constantdegradation, and so the proportion of the ¹⁴C nuclei in the carbon inthe atmosphere on Earth is constant over long periods. The samedistribution ratio n¹⁴C:n¹²C ratio is established in living organisms asis present in the surrounding atmosphere, which stops at death and ¹⁴Cdecomposes at a half life of about 6000 years. Methanol, acetic acidand/or ethanol formed from biomass-derived syngas would be expected tohave a ¹⁴C content that is substantially similar to living organisms.For example, the ¹⁴C:¹²C ratio of the methanol, acetic acid and/orethanol may be from one half to about 1 of the ¹⁴C:¹²C ratio for livingorganisms. In other embodiments, the syngas, methanol, acetic acidand/or ethanol described herein are derived wholly from fossil fuels,i.e. carbon sources produced over 60,000 years ago, may have nodetectable ¹⁴C content.

In another embodiment, the acetic acid used in the hydrogenation stepmay be formed from the fermentation of biomass. The fermentation processpreferably utilizes an acetogenic process or a homoacetogenicmicroorganism to ferment sugars to acetic acid producing little, if any,carbon dioxide as a by-product. The carbon efficiency for thefermentation process preferably is greater than 70%, greater than 80% orgreater than 90% as compared to conventional yeast processing, whichtypically has a carbon efficiency of about 67%. Optionally, themicroorganism employed in the fermentation process is of a genusselected from the group consisting of Clostridium, Lactobacillus,Moorella, Thermoanaerobacter, Propionibacterium, Propionispera,Anaerobiospirillum, and Bacteriodes, and in particular, species selectedfrom the group consisting of Clostridium formicoaceticum, Clostridiumbutyricum, Moorella thermoacetica, Thermoanaerobacter kivui,Lactobacillus delbrukii, Propionibacterium acidipropionici,Propionispera arboris, Anaerobiospirillum succinicproducens, Bacteriodesamylophilus and Bacteriodes ruminicola. Optionally, in this process, allor a portion of the unfermented residue from the biomass, e.g., lignans,may be gasified to form hydrogen that may be used in the hydrogenationstep of the present invention. Exemplary fermentation processes forforming acetic acid are disclosed in U.S. Pat. No. 6,509,180, and U.S.Pub. Nos. 2008/0193989 and 2009/0281354, the entireties of which areincorporated herein by reference.

Examples of biomass include, but are not limited to, agriculturalwastes, forest products, grasses, and other cellulosic material, timberharvesting residues, softwood chips, hardwood chips, tree branches, treestumps, leaves, bark, sawdust, off-spec paper pulp, corn, corn stover,wheat straw, rice straw, sugarcane bagasse, switchgrass, miscanthus,animal manure, municipal garbage, municipal sewage, commercial waste,grape pumice, almond shells, pecan shells, coconut shells, coffeegrounds, grass pellets, hay pellets, wood pellets, cardboard, paper,plastic, and cloth. Another biomass source is black liquor, which is anaqueous solution of lignin residues, hemicellulose, and inorganicchemicals.

U.S. Pat. No. RE 35,377, also incorporated herein by reference, providesa method for the production of methanol by conversion of carbonaceousmaterials such as oil, coal, natural gas and biomass materials. Theprocess includes hydrogasification of solid and/or liquid carbonaceousmaterials to obtain a process gas which is steam pyrolized withadditional natural gas to form syngas. The syngas is converted tomethanol which may be carbonylated to acetic acid. The method likewiseproduces hydrogen which may be used in connection with this invention asnoted above. U.S. Pat. No. 5,821,111, which discloses a process forconverting waste biomass through gasification into syngas, and U.S. Pat.No. 6,685,754, which discloses a method for the production of ahydrogen-containing gas composition, such as a syngas including hydrogenand carbon monoxide, are incorporated herein by reference in theirentireties.

The acetic acid fed to the hydrogenation reactor may also comprise othercarboxylic acids and anhydrides, as well as aldehyde and/or ketones,such as acetaldehyde and acetone. Preferably, the feed stream comprisesacetic acid and ethyl acetate. A suitable acetic acid feed streamcomprises one or more of the compounds selected from the groupconsisting of acetic acid, acetic anhydride, acetaldehyde, ethylacetate, diethyl acetal, diethyl ether, and mixtures thereof. Theseother compounds may also be hydrogenated in the processes of the presentinvention. In some embodiments, the presence of carboxylic acids, suchas propanoic acid or its aldehyde, may be beneficial in producingpropanol. Water may also be present in the acetic acid feed.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078, the entirety of which isincorporated herein by reference. The crude vapor product, for example,may be fed directly to the hydrogenation reactor without the need forcondensing the acetic acid and light ends or removing water, savingoverall processing costs.

The acetic acid may be vaporized at the reaction temperature, followingwhich the vaporized acetic acid may be fed along with hydrogen in anundiluted state or diluted with a relatively inert carrier gas, such asnitrogen, argon, helium, carbon dioxide and the like. For reactions runin the vapor phase, the temperature should be controlled in the systemsuch that it does not fall below the dew point of acetic acid. In oneembodiment, the acetic acid may be vaporized at the boiling point ofacetic acid at the particular pressure, and then the vaporized aceticacid may be further heated to the reactor inlet temperature. In anotherembodiment, the acetic acid is mixed with other gases before vaporizing,followed by heating the mixed vapors up to the reactor inlettemperature. Preferably, the acetic acid is transferred to the vaporstate by passing hydrogen and/or recycle gas through the acetic acid ata temperature at or below 125° C., followed by heating of the combinedgaseous stream to the reactor inlet temperature.

The reactor, in some embodiments, may include a variety ofconfigurations using a fixed bed reactor or a fluidized bed reactor. Inmany embodiments of the present invention, an “adiabatic” reactor can beused; that is, there is little or no need for internal plumbing throughthe reaction zone to add or remove heat. In other embodiments, a radialflow reactor or reactors may be employed as the reactor, or a series ofreactors may be employed with or without heat exchange, quenching, orintroduction of additional feed material. Alternatively, a shell andtube reactor provided with a heat transfer medium may be used. In manycases, the reaction zone may be housed in a single vessel or in a seriesof vessels with heat exchangers therebetween.

In preferred embodiments, the catalyst is employed in a fixed bedreactor, e.g., in the shape of a pipe or tube, where the reactants,typically in the vapor form, are passed over or through the catalyst.Other reactors, such as fluid or ebullient bed reactors, can beemployed. In some instances, the hydrogenation catalysts may be used inconjunction with an inert material to regulate the pressure drop of thereactant stream through the catalyst bed and the contact time of thereactant compounds with the catalyst particles. In some embodiments,multiple catalyst beds are employed in the same reactor or in differentreactors, e.g., in series. For example, in one embodiment, a firstcatalyst functions in a first catalyst stage as a catalyst for thehydrogenation of a carboxylic acid, e.g., acetic acid, to itscorresponding alcohol, e.g., ethanol, and a second bifunctional catalystis employed in the second stage for converting unreacted acetic acid toethanol as well as converting byproduct ester, e.g., ethyl acetate, toadditional products, preferably to ethanol. The catalysts of theinvention may be employed in either or both the first and/or secondstages of such reaction systems.

The hydrogenation in the reactor may be carried out in either the liquidphase or vapor phase. Preferably, the reaction is carried out in thevapor phase under the following conditions. The reaction temperature mayrange from 125° C. to 350° C., e.g., from 200° C. to 325° C., from 225°C. to 300° C., or from 250° C. to 300° C. The pressure may range from 10kPa to 3000 kPa, e.g., from 50 kPa to 2300 kPa, or from 100 kPa to 2000kPa. The reactants may be fed to the reactor at a gas hourly spacevelocity (GHSV) of greater than 500 hr⁻¹, e.g., greater than 1000 hr⁻¹,greater than 2500 hr⁻¹ or even greater than 5000 hr⁻¹. In terms ofranges the GHSV may range from 50 hr⁻¹ to 50,000 hr⁻¹, e.g., from 500hr⁻¹ to 30,000 hr⁻¹, from 1000 hr⁻¹ to 10,000 hr⁻¹, or from 1000 hr⁻¹ to6500 hr⁻¹.

The hydrogenation optionally is carried out at a pressure justsufficient to overcome the pressure drop across the catalytic bed at theGHSV selected, although there is no bar to the use of higher pressures,it being understood that considerable pressure drop through the reactorbed may be experienced at high space velocities, e.g., 5000 hr⁻¹ or6,500 hr⁻¹.

Although the reaction consumes two moles of hydrogen per mole of aceticacid to produce one mole of ethanol, the actual molar ratio of hydrogento acetic acid in the feed stream may vary from about 100:1 to 1:100,e.g., from 50:1 to 1:50, from 20:1 to 1:2, or from 18:1 to 2:1. Mostpreferably, the molar ratio of hydrogen to acetic acid is greater than2:1, e.g., greater than 4:1 or greater than 8:1. For a mixed feedstream, the molar ratio of hydrogen to ethyl acetate may be greater than5:1, e.g., greater than 10:1 or greater than 15:1.

Contact or residence time can also vary widely, depending upon suchvariables as amount of feed stream (acetic acid and/or ethyl acetate),catalyst, reactor, temperature, and pressure. Typical contact timesrange from a fraction of a second to more than several hours when acatalyst system other than a fixed bed is used, with preferred contacttimes, at least for vapor phase reactions, from 0.1 to 100 seconds,e.g., from 0.3 to 80 seconds or from 0.4 to 30 seconds.

In particular, by employing the catalysts of the invention, thehydrogenation of acetic acid and/or ethyl acetate may achieve favorableconversion and favorable selectivity and productivity to ethanol in thereactor. For purposes of the present invention, the term “conversion”refers to the amount of acetic acid or ethyl acetate, whichever isspecified, in the feed that is converted to a compound other than aceticacid or ethyl acetate, respectively. Conversion is expressed as apercentage based on acetic acid or ethyl acetate in the feed. The aceticacid conversion may be at least 20%, more preferably at least 60%, atleast 75%, at least 80%, at least 90%, at least 95% or at least 99%.

During the hydrogenation of acetic acid, ethyl acetate may be producedas a byproduct. Without consuming any ethyl acetate from the mixed vaporphase reactants, the conversion of ethyl acetate would be deemednegative. Some of the catalysts described herein are monofunctional innature and are effective for converting acetic acid to ethanol, but notfor converting ethyl acetate. The use of monofunctional catalysts mayresult in the undesirable build up of ethyl acetate in the system,particularly for systems employing one or more recycle streams thatcontain ethyl acetate to the reactor.

The preferred catalysts of the invention, however, are multifunctionalin that they effectively catalyze the conversion of acetic acid toethanol as well as the conversion of an alkyl acetate, such as ethylacetate, to one or more products other than that alkyl acetate. Themultifunctional catalyst is preferably effective for consuming ethylacetate at a rate sufficiently great so as to at least offset the rateof ethyl acetate production, thereby resulting in a non-negative ethylacetate conversion, i.e., no net increase in ethyl acetate is realized.The use of such catalysts may result, for example, in an ethyl acetateconversion that is effectively 0% or that is greater than 0%. In someembodiments, the catalysts of the invention are effective in providingethyl acetate conversions of at least 0%, e.g., at least 5%, at least10%, at least 15%, at least 20%, or at least 35%.

In continuous processes, the ethyl acetate being added (e.g., recycled)to the hydrogenation reactor and ethyl acetate leaving the reactor inthe crude product preferably approaches a certain level after theprocess reaches equilibrium. The use of a multifunctional catalyst thatcatalyzes the conversion of ethyl acetate as well as acetic acid resultsin a lower amount of ethyl acetate added to the reactor and less ethylacetate produced relative to monofunctional catalysts. In preferredembodiments, the concentration of ethyl acetate in the mixed feed andcrude product is less than 40 wt. %, less than 25 wt. % or less than 15wt. %, after equilibrium has been achieved. In preferred embodiments,the process forms a crude product comprising ethanol and ethyl acetate,and the crude product has an ethyl acetate steady state concentrationfrom 0.1 to 40 wt. %, e.g., from 0.1 to 20 wt. % or from 0.1 to 15 wt.%.

Although catalysts that have high acetic acid conversions are desirable,such as at least 60%, in some embodiments a low conversion may beacceptable at high selectivity for ethanol. It is, of course, wellunderstood that in many cases, it is possible to compensate forconversion by appropriate recycle streams or use of larger reactors, butit is more difficult to compensate for poor selectivity.

Selectivity is expressed as a mole percent based on converted aceticacid and/or ethyl acetate. It should be understood that each compoundconverted from acetic acid and/or ethyl acetate has an independentselectivity and that selectivity is independent of conversion. Forexample, if 60 mole % of the converted acetic acid is converted toethanol, we refer to the ethanol selectivity as 60%. For purposes of thepresent invention, the total selectivity is based on the combinedconverted acetic acid and ethyl acetate. Preferably, total selectivityto ethanol is at least 60%, e.g., at least 70%, or at least 80%, atleast 85% or at least 88%. Preferred embodiments of the hydrogenationprocess also have low selectivity to undesirable products, such asmethane, ethane, and carbon dioxide. The selectivity to theseundesirable products preferably is less than 4%, e.g., less than 2% orless than 1%. More preferably, these undesirable products are present inundetectable amounts. Formation of alkanes may be low, and ideally lessthan 2%, less than 1%, or less than 0.5% of the acetic acid passed overthe catalyst is converted to alkanes, which have little value other thanas fuel.

The term “productivity,” as used herein, refers to the grams of aspecified product, e.g., ethanol, formed during the hydrogenation basedon the kilograms of catalyst used per hour. A productivity of at least100 grams of ethanol per kilogram of catalyst per hour, e.g., at least400 grams of ethanol per kilogram of catalyst per hour or at least 600grams of ethanol per kilogram of catalyst per hour, is preferred. Interms of ranges, the productivity preferably is from 100 to 3,000 gramsof ethanol per kilogram of catalyst per hour, e.g., from 400 to 2,500grams of ethanol per kilogram of catalyst per hour or from 600 to 2,000grams of ethanol per kilogram of catalyst per hour.

In various embodiments of the present invention, the crude ethanolproduct produced by the reactor, before any subsequent processing, suchas purification and separation, will typically comprise unreacted aceticacid, ethanol and water. Exemplary compositional ranges for the crudeethanol product are provided in Table 1. The “others” identified inTable 1 may include, for example, esters, ethers, aldehydes, ketones,alkanes, and carbon dioxide.

TABLE 1 CRUDE ETHANOL PRODUCT COMPOSITIONS Conc. Conc. Conc. Conc.Component (wt. %) (wt. %) (wt. %) (wt. %) Ethanol 5 to 72 15 to 72  15to 70 25 to 65 Acetic Acid 0 to 90 0 to 50  0 to 35  0 to 15 Water 5 to40 5 to 30 10 to 30 10 to 26 Ethyl Acetate 0 to 30 1 to 25  3 to 20  5to 18 Acetaldehyde 0 to 10 0 to 3  0.1 to 3   0.2 to 2   Others 0.1 to10   0.1 to 6   0.1 to 4   —

In one embodiment, the crude ethanol product may comprise acetic acid inan amount less than 20 wt. %, e.g., of less than 15 wt. %, less than 10wt. % or less than 5 wt. %. In terms of ranges, the acetic acidconcentration of Table 1 may range from 0.1 wt. % to 20 wt. %, e.g., 0.1wt. % to 15 wt. %, from 0.1 wt. % to 10 wt. % or from 0.1 wt. % to 5 wt.%. In embodiments having lower amounts of acetic acid, the conversion ofacetic acid is preferably greater than 75%, e.g., greater than 85% orgreater than 90%. In addition, the selectivity to ethanol may also bepreferably high, and is greater than 75%, e.g., greater than 85% orgreater than 90%.

An ethanol product may be recovered from the crude ethanol productproduced by the reactor using the catalyst of the present invention maybe recovered using several different techniques.

The ethanol product may be an industrial grade ethanol comprising from75 to 96 wt. % ethanol, e.g., from 80 to 96 wt. % or from 85 to 96 wt. %ethanol, based on the total weight of the ethanol product. Theindustrial grade ethanol may have a water concentration of less than 12wt. % water, e.g., less than 8 wt. % or less than 3 wt. %. In someembodiments, when further water separation is used, the ethanol productpreferably contains ethanol in an amount that is greater than 96 wt. %,e.g., greater than 98 wt. % or greater than 99.5 wt. %. The ethanolproduct having further water separation preferably comprises less than 3wt. % water, e.g., less than 2 wt. % or less than 0.5 wt. %.

The finished ethanol composition produced by the embodiments of thepresent invention may be used in a variety of applications includingfuels, solvents, chemical feedstocks, pharmaceutical products,cleansers, sanitizers, hydrogen transport or consumption. In fuelapplications, the finished ethanol composition may be blended withgasoline for motor vehicles such as automobiles, boats and small pistonengine aircraft. In non-fuel applications, the finished ethanolcomposition may be used as a solvent for toiletry and cosmeticpreparations, detergents, disinfectants, coatings, inks, andpharmaceuticals. The finished ethanol composition may also be used as aprocessing solvent in manufacturing processes for medicinal products,food preparations, dyes, photochemicals and latex processing.

The finished ethanol composition may also be used as a chemicalfeedstock to make other chemicals such as vinegar, ethyl acrylate, ethylacetate, ethylene, glycol ethers, ethylamines, ethyl benzene, aldehydes,butadiene, and higher alcohols, especially butanol. In the production ofethyl acetate, the finished ethanol composition may be esterified withacetic acid. In another application, the finished ethanol compositionmay be dehydrated to produce ethylene. Any known dehydration catalyst,such as zeolite catalysts or phosphotungstic acid catalysts, can beemployed to dehydrate ethanol, as described in U.S. Pub. Nos.2010/0030002 and 2010/0030001 and WO2010146332, the entire contents anddisclosures of which are hereby incorporated by reference.

Catalyst Regeneration

The catalysts of the invention are particularly robust and have longcatalyst lifetimes. Nevertheless, over periods of extended usage, theactivity of the catalysts of the invention may gradually be reduced.Accordingly, in another embodiment of the invention, the inventionrelates to a process for regenerating a spent hydrogenation catalyst,comprising contacting a carboxylic acid and hydrogen in a hydrogenationreactor with a hydrogenation catalyst under conditions effective to forma hydrogenation product and the spent hydrogenation catalyst; andtreating the spent hydrogenation catalyst with a regenerating medium ata temperature greater than 200° C., optionally from 300° C. to 600° C.,under conditions effective to form a regenerated hydrogenation catalysthaving greater catalytic activity than the spent hydrogenation catalyst,wherein the hydrogenation catalyst comprises a precious metal and one ormore active metals on a support. In this context, by “spent” it is meanta catalyst having reduced conversion and/or reduced selectivity for thedesired product, e.g., ethanol, relative to an earlier usage period forthe same catalyst, wherein the reduced selectivity and/or conversioncannot be recovered by increasing reactor temperature up to designedlimits.

In another embodiment, the invention is to a process for regenerating aspent catalyst comprising (a) contacting a carboxylic acid and hydrogenin a hydrogenation reactor with a hydrogenation catalyst underconditions effective to form a hydrogenation product and the spenthydrogenation catalyst; and (b) treating the spent hydrogenationcatalyst with a regenerating medium at a temperature greater than 200°C., optionally from 300° C. to 600° C., under conditions effective toform a regenerated hydrogenation catalyst having greater catalyticactivity than the spent hydrogenation catalyst, wherein thehydrogenation catalyst comprises a precious metal and one or more activemetals on a support. The treating may occur within the hydrogenationreactor, or external to the hydrogenation reactor. For example, thetreating may occur in a regeneration unit, in which case the processfurther comprises the steps of directing the spent hydrogenationcatalyst from the hydrogenation reactor to the regeneration unit, anddirecting the regenerated hydrogenation catalyst from the regenerationunit to the hydrogenation reactor.

The regenerating medium may vary depending on whether it is desired tomerely “strip” the catalyst, for example of carbonaceous materials, orwhether full regeneration is desired. Depending on the condition of thespent catalyst, the regenerating medium may be selected from steam,oxygen (optionally in the form of air, diluted air or an oxygen/nitrogenmixture optionally with variable O₂/N₂ ratio during regenerationtreatment), or hydrogen. Preferably, the regeneration medium issubstantially free of the carboxylic acid reactant, optionallycomprising less than 10 wt. % carboxylic acids, less than 5 wt. %carboxylic acids, or less than 1 wt. % carboxylic acids, e.g., aceticacid. The treating step may occur, for example, at a pressure rangingfrom 0.5 to 10 bar, e.g., from 0.8 to 8 bar or from 0.9 to 4 bar. Theregenerating may occur, for example, over a period ranging from 10 to200 hours, e.g., from 20 to 150 hours or from 50 to 100 hours.Preferably, the conditions employed in the treating step are sufficientto increase the carboxylic acid conversion, e.g., acetic acidconversion, and/or ethanol selectivity of the resulting regeneratedhydrogenation catalyst by at least 25%, e.g., at least 50%, or at least75%, relative to the conversion and selectivity of the spent catalyst.In another aspect, the spent catalyst has a reduced or lost ethanolselectivity relative to fresh catalyst, and the regenerated catalystrecovers at least 25%, at least 50% or at least 75% of the lost ethanolselectivity. Similarly, the spent catalyst may have a reduced or lostacetic acid conversion relative to fresh catalyst, and the regeneratedcatalyst recovers at least 25%, at least 50% or at least 75% of the lostacetic acid conversion.

If steam is employed as the regeneration medium, it may be desired todry the regenerated hydrogenation catalyst prior to using theregenerated hydrogenation catalyst in the primary hydrogenation process.The drying is optionally performed at a temperature from 10 to 350° C.,e.g., 50 to 250° C., from 70 to 180° C. or from 80 to 130° C., andoptionally at an absolute pressure from 0.5 to 5 bar, e.g., from 0.8 to2 bar, or from 0.9 to 1.5 bar, and optionally over a period of time from10 to 50 hours, e.g., 10 to 20 hours, as described in US Pub. No.2011/0144398, the entirety of which is incorporated herein by reference.

The following examples describe the catalyst and process of thisinvention.

EXAMPLES Example 1 Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A. Preparation of Modified Support: Co(3.75)Sn(3.25)WO₃(12)/SiO₂

A summary of the catalyst preparation protocol is provided in FIG. 1. Ametal impregnation solution was prepared as follows. First, a solutionof tin salt was prepared by adding 8.56 g (0.0414 mol) of SnC₂O₄ (solid)slowly into 41 g (0.328 mol) of 8M HNO₃ in a 300 ml beaker whilestifling. 70 g of DI-H₂O was then added to further dilute the solution.28 g (0.0962 mol) of Co(NO₃)₂.6H₂O solid was then added to the abovesolution with stirring. After the Co salt was completely dissolved,19.47 g (0.079 mol W) of ammonium metatungstate (AMT) was added to theabove solution. The mixture was then stirred at 400 rpm for another 5minutes at room temperature.

The solution was then added to 120 g SiO₂ support in a one-liter roundflask by using incipient wetness techniques to provide a uniformdistribution on the support. After adding the solution, the material wasevacuated to dryness using a rotary evaporator with bath temperature at80° C. and vacuum at 72 mbar for 2 hours, followed by drying at 120° C.for 12 hours under circulating air and calcination at 600° C. for 8hours. Temperature Program: Increase from room temperature to 160° C. at3° C./min ramp, hold at 160° C. for 2 hours; increase from 160° C. to600° C. at 3° C./min ramp, and hold at 600° C. for 8 hours.

B. Impregnation of Modified Support:Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A solution of tin salt was prepared by adding 6.28 g (0.0304 mol) ofSnC₂O₄ (solid) slowly into 38.08 g (0.305 mol) of 8M HNO₃ in a 300 mlbeaker while stifling. 13 g of DI-H₂O was added to further dilute thesolution. 20.57 g (0.0707 mol) of Co(NO₃)₂.6H₂O was added to thesolution with stirring. A solution of platinum oxalate wassimultaneously prepared by diluting 11.72 g (6.08 mmol Pt) of platinumoxalate (Pt: 10.12 wt. %) with 15 g of DI-H₂O. The diluted platinumoxalate was added to above Co/Sn solution.

The resulting solution was then added to 100 g of the modified supportpellets (CoSnWO₃/SiO₂) in a one-liter round flask by using incipientwetness techniques to provide a uniform distribution on the support.After adding the solution, the material was evacuated to dryness with arotary evaporator at a bath temperature of 80° C. and vacuum at 72 mbarfor 2 hours, followed by drying at 120° C. for 12 hours undercirculating air and calcination at 350° C. for 8 hours. TemperatureProgram: increase from room temperature to 160° C. at 3° C./min ramp,hold at 160° C. for 2 hours, increase for 160° C. to 350° C. at 3°C./min ramp, hold at 350° C. for 8 hours. The impregnation solution waskept stifling during its addition to the support. The flask containingthe support was continuously rotated during impregnation to ensureuniform distribution of the added liquid.

Example 2 Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A. Preparation of Modified Support: Co(3.75)Sn(3.25)WO₃(12)/SiO₂

A metal impregnation solution was prepared as follows. First, a solutionof tin salt was prepared by adding 15.67 g (0.045 mol) of Sn(IV)Cl₄.5H₂O(solid) into 100 g of DI-H₂O. 30.23 g (0.104 mol) of Co(NO₃)₂.6H₂O(solid) was added to the solution with stifling. After the cobalt saltwas completely dissolved, 21.03 g (0.085 mol of W) of AMT was added tothe solution. The mixture was then stirred at 400 rpm for another 5minutes at room temperature.

The resulting solution was then added to 129.6 g. SiO₂ support in aone-liter round flask by using incipient wetness techniques to provide auniform distribution on the support. After adding the metal solution,the material was evacuated to dryness using a rotary evaporator withbath temperature at 80° C. and vacuum at 72 mbar for 2 hours, followedby drying at 120° C. for 12 hours under circulating air and calcinationat 600° C. for 8 hours. Temperature Program: Increase from roomtemperature to 160° C. at 3° C./min ramp, hold at 160° C. for 2 hours;increase from 160° C. to 600° C. at 3° C./min ramp, and hold at 600° C.for 8 hours.

B. Impregnation of Modified Support:Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A metal impregnation solution was prepared. A tin salt solution wasprepared by dissolving 4.8 g (13.69 mmol) of Sn(IV)Cl₄.5H₂O (solid) into29.4 g of DI-H₂O. 9.26 g (31.8 mmol) of Co(NO₃)₂.6H₂O (solid) was addedto the solution with stifling. A platinum salt solution wassimultaneously prepared by dissolving 1.4 g (2.7 mmol Pt) ofH₂PtCl₆.XH₂O (solid, Pt: 38.2 wt. %) into 14.7 g of DI-H₂O. The platinumsalt solution was added to the above Co/Sn solution. The mixture wasstirred at 400 rpm for 5 minutes at room temperature.

The resulting solution was then added to 45.04 g of CoSnWO₃/SiO₂ pelletsformed as described above in a one-liter round flask by using incipientwetness techniques to provide a uniform distribution on the support.After adding the metal solution, the material was evacuated to drynesswith a rotary evaporator at a bath temperature of 80° C. and vacuum at72 mbar for 2 hours, followed by drying at 120° C. at 12 hours undercirculating air and calcination at 350° C. for 8 hours. Temperatureprogram: increase from room temperature to 160° C. at 3° C./min ramp,hold at 160° C. for 2 hours, increase from 160° C. to 350° C. at 3°C./min ramp, and hold at 350° C. for 8 hours.

Example 3 Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A. Preparation of Modified Support: Co(3.75)Sn(3.25)WO₃(12)/SiO₂

A metal impregnation solution was prepared as follows. First, a solutionof tin salt was prepared by dissolving 2.476 g of Sn(II)Cl₂.2H₂O (solid)into the 25 g of DI-H₂O. 7.559 g of Co(NO₃)₂.6H₂O solid was add to thesolution with stifling. After the Co salt was completely dissolved,5.257 g of AMT was added to the solution. The mixture was then stirredat 400 rpm for another 5 minutes at room temperature.

The resulting solution was then added to 32.4 g SiO₂ support in aone-liter round flask by using incipient wetness technique to provide auniform distribution on the support. After adding the metal solution,the material was evacuated to dryness using a rotary evaporator withbath temperature at 80° C. and vacuum at 72 mbar for 2 hours, followedby drying at 120° C. for 12 hours under circulating air and calcinationat 600° C. for 8 hours. Temperature Program: increase from roomtemperature to 160° C. at 3° C./min ramp, hold at 160° C. for 2 hours;increase from 160° C. to 600° C. at 3° C./min ramp, hold at 600° C. for6 hours.

B. Impregnation of Modified Support:Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A tin salt solution was prepared by dissolving 0.619 g of Sn(II)Cl₂.2H₂O(solid) into 6 g of DI-H₂O. 1.89 g of Co(NO₃)₂.6H₂O solid was add to thesolution with stirring. A platinum salt solution was simultaneouslyprepared by dissolving 0.286 g of H₂PtCl₆.xH₂O (solid, Pt: 38.2 wt. %)into 3 g of DI-H₂O. The platinum salt solution was added to the aboveCo/Sn solution. The mixture was then stirred at 400 rpm for another 5minutes at room temperature.

The resulting solution was then added to 9.191 g of CoSnWO₃/SiO₂ pelletsformed as described above in a one-liter round flask by using incipientwetness technique to provide a uniform distribution on the support.After adding the metal solution, the material was evacuated to drynesswith a rotary evaporator at a bath temperature of 80° C. and vacuum at72 mbar for 2 hours, followed by drying at 120° C. for 12 hours undercirculating air and calcination at 350° C. for 8 hours. TemperatureProgram: increase from room temperature to 160° C. at 3° C./min ramp,hold at 160° C. for 2 hours; increase from 160° C. to 350° C. at 3°C./min ramp, hold at 350° C. for 6 hours.

Example 4 Pt(1.09)Co(2.5)Sn(2.1)/CoSnWO₃/SiO₂ Preparation of ModifiedSupport: Co(2.5)Sn(2.1)WO₃(9)/SiO₂

A metal impregnation solution was prepared as follows. First, a solutionof tin salt was prepared by adding 1.493 g of SnC₂O₄ (solid) slowly intothe 14 g of 8M HNO₃ in a 200 mL beaker while stirring. 19 g of DI-H₂Owas then added to further dilute the solution. 5.04 g of Co(NO₃)₂.6H₂Osolid was then add to above solution with stifling. After the Co saltwas completely dissolved, 3.943 g of AMT was added to above solution.The mixture was then stirred at 400 rpm for another 5 minutes at roomtemperature.

The solution was then added to 34.56 g SiO₂ support in a one-liter roundflask by using incipient wetness technique to provide a uniformdistribution on the support. After adding the solution, the material wasevacuated to dryness with rotary evaporator with bath temperature at 80°C. and vacuum at 72 mbar for 2 hours, followed by drying at 120° C. for12 hours under circulating air and calcination at 600° C. for 8 hoursTemperature Program: increase from room temperature to 160° C. at 3°C./min ramp, hold at 160° C. for 2 hours; Increase from 160° C. to 550°C. at 3° C./min ramp, and hold at 550° C. for 8 hours.

B. Impregnation of Modified Support: Pt(1.09)Co(2.5)Sn(2.1)/CoSnWO₃/SiO₂

A solution of tin salt was prepared by adding 0.373 g of SnC₂O₄ (solid)slowly into the 3 g of 8M HNO₃ in a 50 mL beaker while stirring. 3 g ofDI-H₂O was added to further dilute the solution. 1.2598 g ofCo(NO₃)₂.6H₂O was add to the solution with stirring. A solution of Ptoxalate was simultaneously prepared by diluting 1 g of Pt oxalate (Pt:10.12 wt. %) with 1 g of DI-H₂O. Then, the diluted Pt oxalate was addedto above Co/Sn solution.

The resulting solution was then added to 9.44 g of the modified supportpellets (CoSnWO₃/SiO₂) in a round flask by using incipient wetnesstechnique to provide a uniform distribution on the support. After addingthe solution, the material was evacuated to dryness with a rotaryevaporator at bath temperature of 80° C. and vacuum at 72 mbar for 2hours, followed by drying at 120° C. for 12 hours under circulating airand calcination at 350° C. for 8 hours. Temperature Program: increasefrom room temperature to 160° C. at 3° C./min ramp, hold at 160° C. for2 hours; Increase from 160° C. to 350° C. at 3° C./min ramp, and hold at350° C. for 8 hours. The flask containing the support was continuouslyrotated during impregnation to ensure uniform distribution of the addedliquid.

Example 5 Pt(1.09)Co(1.4)Sn(1.2)/CoSnWO₃/SiO₂

A. Preparation of Modified Support: Co(3.75)Sn(3.25)WO₃(12)/SiO₂

A metal impregnation solution was prepared as follows. First, a solutionof tin salt was prepared by adding 2.31 g of SnC₂O₄ (solid) slowly intothe 11 g of 8M HNO₃ in a 200 mL beaker while stirring. 19 g of DI-H₂Owas then added to further dilute the solution. 7.559 g of Co(NO₃)₂.6H₂Osolid was then add to above solution with stifling. After the Co saltwas completely dissolved, 5.26 g of AMT was added to above solution. Themixture was then stirred at 400 rpm for another 5 minutes at roomtemperature.

The solution was then added to 32.4 g SiO₂ support in a one-liter roundflask by using incipient wetness technique to provide a uniformdistribution on the support. After adding the solution, the material wasevacuated to dryness with rotary evaporator with bath temperature at 80°C. and vacuum at 72 mbar for 2 hours, followed by drying at 120° C. for12 hours under circulating air and calcination at 600° C. for 8 hoursTemperature Program: increase from room temperature to 160° C. at 3°C./min ramp, hold at 160° C. for 2 hours; Increase from 160° C. to 550°C. at 3° C./min ramp, and hold at 550° C. for 8 hours.

B. Impregnation of Modified Support: Pt(1.09)Co(1.4)Sn(1.2)/CoSnWO₃/SiO₂

A solution of tin salt was prepared by adding 0.213 g of SnC₂O₄ (solid)slowly into the 3 g of 8M HNO₃ in a 50 mL beaker while stirring. 3.5 gof DI-H₂O was added to further dilute the solution. 0.706 g ofCo(NO₃)₂.6H₂O was add to the solution with stirring. A solution of Ptoxalate was simultaneously prepared by diluting 1.09 g of Pt oxalate(Pt: 10.00 wt. %) with 1 g of DI-H₂O. Then, the diluted Pt oxalate wasadded to above Co/Sn solution.

The resulting solution was then added to 9.63 g of the modified supportpellets (CoSnWO₃/SiO₂) in a round flask by using incipient wetnesstechnique to provide a uniform distribution on the support. After addingthe solution, the material was evacuated to dryness with a rotaryevaporator at bath temperature of 80° C. and vacuum at 72 mbar for 2hours, followed by drying at 120° C. for 12 hours under circulating airand calcination at 350° C. for 8 hours. Temperature Program: increasefrom room temperature to 160° C. at 3° C./min ramp, hold at 160° C. for2 hours; Increase from 160° C. to 350° C. at 3° C./min ramp, and hold at350° C. for 8 hours. The flask containing the support was continuouslyrotated during impregnation to ensure uniform distribution of the addedliquid.

Example 6 Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A. Preparation of Modified Support: Co(3.75)Sn(3.25)WO₃(16)/SiO₂

A metal impregnation solution was prepared as follows. First, a solutionof tin salt was prepared by adding 2.31 g of SnC₂O₄ (solid) slowly intothe 11 g of 8M HNO₃ in a 200 mL beaker while stirring. 19 g of DI-H₂Owas then added to further dilute the solution. 7.559 g of Co(NO₃)₂.6H₂Osolid was then add to above solution with stifling. After the Co saltwas completely dissolved, 7.01 g of AMT was added to above solution. Themixture was then stirred at 400 rpm for another 5 minutes at roomtemperature.

The solution was then added to 30.8 g SiO₂ support in a one-liter roundflask by using incipient wetness technique to provide a uniformdistribution on the support. After adding the solution, the material wasevacuated to dryness with rotary evaporator with bath temperature at 80°C. and vacuum at 72 mbar for 2 hours, followed by drying at 120° C. for12 hours under circulating air and calcination at 600° C. for 8 hoursTemperature Program: increase from room temperature to 160° C. at 3°C./min ramp, hold at 160° C. for 2 hours; Increase from 160° C. to 550°C. at 3° C./min ramp, and hold at 550° C. for 8 hours.

B. Impregnation of Modified Support:Pt(1.09)Co(3.75)Sn(3.25)/CoSnWO₃/SiO₂

A solution of tin salt was prepared by adding 0.578 g of SnC₂O₄ (solid)slowly into the 3.5 g of 8M HNO₃ in a 50 mL beaker while stifling. 2.5 gof DI-H₂O was added to further dilute the solution. 1.89 g ofCo(NO₃)₂.6H₂O was add to the solution with stifling. A solution of Ptoxalate was simultaneously prepared by diluting 1.09 g of Pt oxalate(Pt: 10.00 wt. %) with 1 g of DI-H₂O. Then, the diluted Pt oxalate wasadded to above Co/Sn solution.

The resulting solution was then added to 9.191 g of the modified supportpellets (CoSnWO₃/SiO₂) in a round flask by using incipient wetnesstechnique to provide a uniform distribution on the support. After addingthe solution, the material was evacuated to dryness with a rotaryevaporator at bath temperature of 80° C. and vacuum at 72 mbar for 2hours, followed by drying at 120° C. for 12 hours under circulating airand calcination at 350° C. for 8 hours. Temperature Program: increasefrom room temperature to 160° C. at 3° C./min ramp, hold at 160° C. for2 hours; Increase from 160° C. to 350° C. at 3° C./min ramp, and hold at350° C. for 8 hours. The flask containing the support was continuouslyrotated during impregnation to ensure uniform distribution of the addedliquid.

Example 7 Performance Tests

The catalysts of Examples 1-6 were fed to a test unit using one of thefollowing running conditions.

Reactor System and Catalytic Testing Conditions.

The test unit comprised four independent tubular fixed bed reactorsystems with common temperature control, pressure and gas and liquidfeeds. The reactors were made of ⅜ inch (0.95 cm) 316 SS tubing, andwere 12⅛ inches (30.8 cm) in length. The vaporizers were made of ⅜ inch(0.95 cm) 316 SS tubing and were 12⅜ inches (31.45 cm) in length. Thereactors, vaporizers, and their respective effluent transfer lines wereelectrically heated (heat tape).

The reactor effluents were routed to chilled water condensers andknock-out pots. Condensed liquids were collected automatically, and thenmanually drained from the knock-out pots as needed. Non-condensed gaseswere passed through a manual back pressure regulator (BPR) and thenscrubbed through water and vented to the fume hood. For each Example, 15ml of catalyst (3 mm pellets) was loaded into reactor. Both inlet andoutlet of the reactor were filled with glass beads (3 mm) to form thefixed bed. The following running conditions for catalyst screening wereused: T=275° C., P=300 psig (2068 kPag), [Feed]=0.138 ml/min (pumprate), and [H₂]=513 sccm, gas-hourly space velocity (GHSV)=2246 hr⁻¹.The mixed feed composition used for testing are summarized in the Table2.

TABLE 2 Mixed Feed Composition for Catalyst Performance Evaluation EthylDiethyl H₂O Acetaldehyde Ethanol Acetate Acetic Acid Acetal (wt. %) (wt.%) (wt. %) (wt. %) (wt. %) (wt. %) 0.65 0.55 5.70 20.72 69.92 2.45

Running Condition 1: Catalyst was fed to a test unit in the mannerdescribed above for Examples 1-6, using the feed composition of TABLE 2.

Running Condition 2: Similar to Running Condition 1, except for catalystusage. 10 mL of catalyst instead of 15 mL of catalyst was used resultingin an increase in superficial velocity to 3367 hr⁻¹.

The crude product was analyzed by gas chromatograph (Agilent GC Model6850), equipped with a flame ionization detector. The GC analyticalresults of the liquid product effluent, excluding water, are providedbelow in TABLE 3. Diethyl ether and acetone were detected inconcentrations were less than 0.1 wt. % respectively.

TABLE 3 Liquid Product Effluent Compositions Examples 1-6 Running EtOHEtOAc AcH HOAc Acetal Condition Ex (wt. %) (wt. %) (wt. %) (wt. %) (wt.%) 1 1 64.9 12.8 0.9 0.4 0.1 2 1 52.5 20.9 0.8 0.8 0.1 2 2 58.2 17.7 0.80.5 0.3 1 3 63.1 14.1 0.8 0.2 0.1 1 4 59.8 16.5 0.8 1.1 0.1 1 5 60.116.1 0.9 0.6 0.1 1 6 64.1 12.6 0.9 0.3 >0.1

Catalyst performance results were then calculated and are provided belowin TABLE 4.

TABLE 4 Catalyst Performance Data Obtained Under Mixed Feed ConditionsExamples 1-6 HOAc EtOAc EtOH EtOH EtOH Running Conv. Conv. Select. Prod.Prod. Condition Ex (%) (%) (mol %) (g/kg/h) (g/L/h) 1 1 99.5 38.1 96.5612.5 326.8 2 1 98.8 0.6 89.1 868.2 396.5 2 2 99.2 14.6 93.4 879.8 407.41 3 99.7 32.9 94.9 605.2 313.7 1 4 98.5 18.8 95.6 619.3 281.7 1 5 99.224.7 95.2 591.3 298.1 1 6 99.6 40.6 92.3 573.3 326.0XRD Characterization

The catalysts from Examples 1-6 were also characterized by X-raydiffraction (XRD). XRD patterns of the samples were obtained using aRigaku D/Max Ultima II Powder X-ray Diffractometer employing Cu Karadiation. The X-ray tube was operated at 40 kV and 40 mA. The majorphase of the XRD for both catalysts were identified to containmonoclinic CoWO₄ (cobalt tungstate) as the major phase (ICSD-15851). AnXRD pattern for the catalyst of Example 1 is shown in FIG. 2.

An x-ray diffraction pattern substantially as shown in Table 5:

TABLE 5 2θ d-spacing (Å) Relative Intensity 15.81 5.60 8.70 19.13 4.6428.90 23.91 3.72 17.80 24.84 3.58 31.00 30.75 2.91 100.00 31.61 2.8312.30 36.44 2.46 28.00 38.65 2.33 5.10 41.55 2.17 14.30 44.37 2.04 11.9045.99 1.97 4.90 48.82 1.86 3.70 50.74 1.80 4.10 52.21 1.75 11.30 54.081.69 29.40 61.75 1.50 12.30 65.06 1.43 20.00 68.77 1.36 2.70 71.91 1.313.10

A catalyst comprising monoclinic cobalt tungstate, wherein said catalysthas an x-ray diffraction pattern in which above 2θ=10°, there is a localmaximum having a characteristic full width at a half maximum at each of:a 2θ value in the range from 18.73 to 19.53°; a 2θ value in the rangefrom 24.25 to 25.43°; a 2θ value in the range from 30.29 to 31.21°; a 2θvalue in the range from 35.93 to 36.95°; a 2θ value in the range from53.55 to 54.61°; a 2θ value in the range from 64.45 to 65.67°.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseskilled in the art. All publications and references discussed above areincorporated herein by reference. In addition, it should be understoodthat aspects of the invention and portions of various embodiments andvarious features recited may be combined or interchanged either in wholeor in part. In the foregoing descriptions of the various embodiments,those embodiments which refer to another embodiment may be appropriatelycombined with other embodiments as will be appreciated by one skilled inthe art. Furthermore, those skilled in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing for producing ethanol, comprisingcontacting a feed stream comprising acetic acid, and/or ethyl acetate,and hydrogen in a reactor at an elevated temperature in the presence ofa catalyst under conditions effective to form ethanol, wherein thecatalyst comprises a precious metal and one or more active metals on amodified support, wherein the modified support comprises: (i) supportmaterial; (ii) a support modifier comprising an oxide of tungsten,molybdenum or vanadium in an amount from 0.1 to 50 wt. %, and (iii) atleast one of the one or more active metals.
 2. The process of claim 1,wherein the precious metal is selected from the group consisting ofrhodium, rhenium, ruthenium, platinum, palladium, osmium, iridium andgold.
 3. The process of claim 1, wherein the precious metal is selectedfrom the group consisting of palladium, platinum, and rhodium.
 4. Theprocess of claim 1, wherein the precious metal is present in an amountfrom 0.05 to 10 wt. %.
 5. The process of claim 1, wherein the supportmodifier is present in an amount from 0.1 wt. % to 40 wt. %.
 6. Theprocess of claim 1, wherein the one or more active metals are selectedfrom the group consisting of copper, iron, cobalt, vanadium, nickel,titanium, zinc, chromium, molybdenum, tungsten, tin, lanthanum, cerium,and manganese.
 7. The process of claim 1, wherein the one or more activemetals are selected from the group consisting of copper, iron, cobalt,nickel, chromium, molybdenum, tungsten and tin.
 8. The process of claim1, wherein the one or more active metals are present in an amount from0.1 to 15 wt. %.
 9. The process of claim 1, wherein the support modifiercomprises tin and is free of tin tungstate.
 10. The process of claim 1,wherein the support material is selected from the group consisting ofsilica, alumina, titania, silica/alumina, pyrogenic silica, high puritysilica, zirconia, carbon, zeolites and mixtures thereof.
 11. The processof claim 1, wherein the feed stream further comprises ethyl acetate inan amount greater than 5 wt. %.